Need advice regarding a deal

[Kajal Aggarwal]

We entered into contract with a 3bed/1bath 1000sq ft property that was listed as R3 zoned. We based our purchase price on the future potential to build a triplex. 10 days later, we found out that it is R2 zoned and the listing has wrong info. We went back to the sellers and asked for 100k price reduction based on comps for 3bed/1bath. We still have our appraisal and loan contingencies. 

We feel guilty for realizing this after being in contract for 14 days and don't want to back out as everyone (Both sides agents, loan officer and us) have spent so much time in trying to close. At the same time, we don't want to over pay. Looking for suggestions from experienced folks here.